1. Field of the Invention
The present invention relates to a structure for preventing glass from breaking and a plasma display panel (hereinafter referred to as “PDP”) device using this structure.
2. Description of the Related Art
A rule that all glass Braun tubes (cathode-ray tubes) should be shatterproof and impenetrable-(resistant to electric shock caused by a hole larger in size than a finger) in an impact resistance test due to dropping of a steel ball has been provided by safety standards (UL standards, the Law of Radio Regulations, etc.) for television sets and display devices. It was therefore necessary to design panel glass to be thick.
With respect to such a CRT glass panel, Unexamined Japanese Patent Publications No. Hei. 6-333515 and 6-333517, etc. have disclosed a glass Braun tube in which a synthetic resin protective film (a film of thermosetting urethane resin and polyester) having self-repairing characteristic is laminated as a weight-reducing unit in order to prevent the glass panel from becoming thick. The disclosed glass Braun tube, however, is only aimed at shatterproof characteristic. There was no description about prevention of the glass panel substrate from breaking. That is, the disclosed glass Braun tube was not provided for preventing the glass panel substrate from breaking.
On the other hand, Unexamined Japanese Patent Publication No. Hei. 11-174206 has described a protective filter for protecting an internal glass substrate of a flat panel display (any one of various kinds of LCDs and PDPs). As the protective filter, a front protection plate made of a transparent resin sheet was disposed at a distance of 10 mm or less from the display to thereby protect glass of the panel itself. According to this configuration, however, there was an air layer between the glass panel and the protection plate. Hence, there were a lot of problems in double reflection of external light, increase in reflectance, lowering of image sharpness due to parallax, and so on. In addition, because there was an air layer, dust, cigarette tar or the like was accumulated in the gap portion of the air layer. Hence, there was a problem that it was difficult to clean the gap portion.
Moreover, in the PDP in which both increase in size and reduction in weight are important, the thickness of the panel itself has a tendency to decrease. Setting the protective filter in a place far from the panel produces the reverse effect. That is, the known technique did not produce any thin and lightweight protective film for preventing the panel in the PDP large-size display from breaking.
In such a PDP, electric discharge is produced in rare gas, particularly gas mainly containing neon, enclosed in the inside of the panel, so that fluorescent substances of R, G and B provided in a cell in the inside of the panel are made luminescent by vacuum ultraviolet rays generated in the electric discharge. In the process of luminescence, electromagnetic wave and near infrared rays unnecessary for the operation of the PDP are emitted simultaneously. Particularly, electromagnetic wave emitted from the PDP needs to be shielded because radiant electromagnetic wave is restricted by VCCT, FCC, etc. and because there is recently a fear that electromagnetic wave has bad influence on the human body.
With respect to near infrared rays, the wavelength range of near infrared rays emitted from the PDP is from about 800 to about 1,200 nm. On the other hand, in most cases, a light-receiving element of an infrared sensor used in a remote controller for a household electrical product, a karaoke machine, an audio-video apparatus or the like has a reception sensitivity peak in a range of from about 700 to about 1,300 nm. For this reason, there is a problem that near infrared rays emitted from the PDP may cause malfunction of the remote controller. It is therefore necessary to cut off near infrared rays emitted from the PDP.
From such background, a filter for cutting off electromagnetic wave and near infrared rays emitted from the PDP has been discussed. For example, as filters for shielding electromagnetic wave, there are known: a film having metal mesh embedded therein; a glass or acrylic plate subjected to a patterning mesh process by etching; a plate formed in such a manner that a film having metal mesh embedded therein or a film subjected to a patterning mesh process by etching is stuck to a glass or acrylic plate; and a transparent multilayer thin-film laminate of a multilayer structure formed in such a manner that each metal thin-film layer is put between transparent thin-film layers. As filters for shielding near infrared rays, there have been already discussed filters constituted by combination of near infrared-absorbing materials such as near infrared absorbing color matters and Cu-complex phosphoric ester-based polymers.
Such a shield filter is, however, generally arranged as a front protection plate in a position at a distance of 10 mm or less from the PDP. That is, the shield filter is not directly stuck onto the PDP panel by a transparent pressure sensitive adhesive agent. This is because the glass substrate in the PDP panel is broken very easily and because the shield filter is arranged in a position far by a distance of from several mm to 10 mm from the PDP panel so that the shield filter can serve also as a front protection filter.